In recent years, research into nanotechnology and nanomanufacturing has been increasing. Of particular interest are nanostructured electrode materials, which may be used in unconventional energy sources such as dye sensitized solar cells, solid oxide fuel cells, and microbial fuel cells.
More than seventy percent of the total power consumed in the world is produced by burning fossil fuel. However, because of the continuously increasing cost of fossil fuel, and concerns about global warming, the importance of developing alternative energy sources has greatly increased. Several alternative sources of energy such as wind, solar, hydro, and nuclear have been explored over the last several decades. Among these unconventional energy sources, solar and nuclear sources are considered the most promising. Because the production of energy from nuclear sources requires building an extensive infrastructure, and has suffered from negative public perception, solar energy remains the most preferred and environmentally friendly alternative to conventional fossil energy sources.
Although interest in solar energy is increasing, solar energy is still not able to compete fully with fossil fuel energy sources because of a number of material challenges. For example, conventional silicon-based solar cells require high-purity, defect free silicon. The cost of producing such high-purity silicon is significant. Coupled with low energy conversion efficiency, the cost of power produced by these cells is still several times more than power produced by conventional energy sources. Because of these issues, the current major challenge in this field is to radically reduce the overall cost of delivered solar electricity by significantly lowering the cost of the cell and improving its energy conversion efficiency.
In this context, Dye Sensitized Solar Cells (DSSCs) may be a viable alternative to the more expensive first-generation inorganic solar cells, in terms of both efficiency and cost-effectiveness. DSSCs operate through a process that is similar in many respects to photosynthesis, the mechanism by which green plants derive chemical energy from sunlight. The DSSC uses an organic dye to absorb light energy in the visible region of the electromagnetic spectrum. This dye then “injects” electrons into the semiconductor base, which enhances electron collection and improves the photovoltage and photocurrent characteristics of the solar cell.
Until recently the most common DSSC platforms under investigation were based on electrodes consisting of sintered semiconducting nanoparticles (mostly TiO2 or ZnO) coated with an organic dye. The dye molecules absorb light in the visible region of the electromagnetic spectrum and then “inject” electrons into the semiconductor electrode. Nanoparticle-based DSSCs rely on trap-limited diffusion through the semiconductor nanoparticles for the subsequent electron transport. This is a slow transport mechanism that limits device efficiency, especially at longer (less energetic) wavelengths, because recombination events become more likely. It is therefore desirable to develop other types of electrodes to overcome the problems associated with conventional DSSCs.